Field of the Invention
This invention relates to optical fibers for an optical fiber cable for use as transmission lines in communication systems and particularly to such optical fibers of which transmission loss is not increased over a prolonged period of time.
It has been recognized that the loss of optical fibers is increased in the range of long wavelengths a long period of time, for example, 5 to 10 years, after an optical fiber cable is installed. It is thought that this phenomenon arises from the fact that a small amount of hydrogen gas (H.sub.2), generated from cured silicone rubber constituting the coating on the optical fiber, is turned to hydroxyl radical (OH) over a long period of time which hydroxyl radical causes the loss of the optical fiber to increase in the range of not less than 1.4 um wavelength.
It has been found that the small amount of hydrogen gas is generated from non-crosslinked Si-H contained in the curing agent contained in the cured silicone rubber. Therefore, it has been found that the reduction or elimination of the residual Si-H in the cured silicone rubber prevents the increase of the loss of the optical fiber.